RICE is an acronym for Rest, Ice, Compression and Elevation. This is done to relieve symptoms and will not cure the underlying injury.
The problem with arthritis is that too much rest causes stiffness and not enough rest causes irritation of the joint. This will vary from person to person and you will need to work out what is right for you. The period of rest should be long enough for you to be able to use your knee with the majority of function restored and pain essentially gone. Resting for more than 20 minutes tends to allow the knee to stiffen up in most people though.
Ice is excellent at reducing the inflammatory response and the pain from heat generated. The traditional method od using ice is to apply it for 20 minutes each hour. There is actually no maximum amount of ice that is safe as long as the skin is not damaged with ‘localised ischaemia’ or frostbite. To avoid this the ice is usually placed in a towel before applying it to the area. If it is a very hot day, or the knee is very inflamed, using ice for longer is often safe. Generally speaking the ice can be left on until the skin under it feels cool to touch. The ice should be removed until the skin warms up to normal temperature and then can be applied again.
Compression helps to reduce oedema (swelling) from the inflammatory process. Although some swelling is inevitable, too much swelling results in significant loss of function and pain from stretching the joint capsule.
An elastic bandage or neoprene type knee guard is ideal. This also helps provide proprioceptive feedback from the area to the brain.
Elevation reduces swelling by allowing the blood in the veins to drain back into the heart. The leg needs to be elevated above the heart so you will need to lie down and raise the leg on a couple of pillows. Sitting with your foot up on a chair elevates it a bit but the knee is still below the heart so the venous blood cannot drain out of the leg properly.